Adding test for broken "set every", see #1430

To test, use:
> scripted tests/set-every

sbt/src/sbt-test/tests/set-every/build.sbt

@@ -0,0 +1,16 @@
+val a = project.settings(version := "2.8.1")
+
+val trySetEvery = taskKey[Unit]("Tests \"set every\"")
+
+trySetEvery := {
+        val s = state.value
+        val extracted = Project.extract(s)
+        import extracted._
+        val allProjs = structure.allProjectRefs
+        val Some(aProj) = allProjs.find(_.project == "a")
+        val aVer = (version in aProj get structure.data).get
+        if (aVer != "1.0") {
+          println("Version of project a: " + aVer + ", expected: 1.0")
+          error("\"set every\" did not change the version of all projects.")
+        }
+}

sbt/src/sbt-test/tests/set-every/test

@@ -0,0 +1,3 @@
+> set every version := '"1.0"'
+> trySetEvery
+